The present invention relates to the field of analytical test elements and methods of making same using ultrasonic or laser energy.
The art of analytical chemistry has been greatly advanced since biochemistry began emerging as a primary scientific frontier, requiring increasingly sophisticated analytical methods and tools to solve problems, the solutions to which were never before attempted. Likewise, the medical profession has lent impetus to the growth of analytical chemistry, emphasizing both high precision and speed in obtaining results. The remarkable progress that has occurred in analytical chemistry has been still further spurred by industries such as brewing, chemical manufacturing, and the food industry.
To satisfy the needs of these expanding technologies, a myriad of analytical procedures, compositions and apparatuses has evolved, including solution chemistry techniques, automated machinery and the so-called reagent test strips. It is to the last of these that the present invention is primarily directed. The reagent strip devices are useful in manual and automated diagnostic systems, and, more particularly, multilayer analytical elements are useful in the qualitative and quantitative determination of body fluid constituents and medicaments present in such body fluids.
Test devices in the form of test strips and similar solid state analytical elements have become commonplace in the analysis of various types of samples, particularly biological fluids. Test strips designed for detecting clinically significant substances in biological fluids, such as serum and urine, have been advantageous in the diagnosis of disease and have enabled more prompt treatment of a variety of conditions.
Reagent strip test devices enjoy wide use in many analytical applications because of their relatively low cost, ease of utilization and speed in obtaining results. In medicine, for example, numerous physiological functions can be monitored merely by dipping reagent strips into a sample of body fluid, such as urine, and observing a detectable response such as a change in color or a change in the amount of light reflected from or absorbed by the strip.
Test strips of various types have been known and used for many years in a wide variety of fields, from the most familar pH test paper devices to in vitro diagnostic devices for glucose, protein, occult blood and the like (see U.S. Pat. Nos. 3,164,534; 3,485,587 and 3,012,976). Reagent compositions found in such test strips, often having limited sensitivity, interact with the constituent or constituents to be determined by direct chemical reaction and are applied to the detection of substances that may be present in liquid samples in very small amounts.
With regard to such reagent test strips, many different chemical reactions have been devised for detecting body fluid components. Many of these reactions produce a detectable response which is quantitative or at least semiquantitative. Thus, by measuring the response after a predetermined time, the analyst can obtain not only a positive indication of the presence of a particular constituent in a test sample, but also an estimate of how much of the constituent is present. Such strips provide the physician with a facile diagnostic tool as well as the ability to gauge the extent of disease or body malfunction.
Test devices usually comprise one or more carrier matrices, such as absorbent paper, having incorporated with them a particular reagent or reactant system which manifests some change, typically color, in the presence of a specific test sample component. Depending on the reactant system incorporated with a particular matrix, these devices can detect the presence of glucose, ketone bodies, bilirubin, urobilinogen, occult blood, nitrite, and other substances. The specific color change and the intensity of the color observed within a specific time range after contacting the strip with the sample is indicative of the presence of a particular component and its concentration in the sample. Some of these test devices and their reactant systems are set forth in U.S. Pat. Nos. 3,123,443; 3,212,855; 3,814,668; 3,164,534; 2,981,606; 3,298,789; and 3,092,465.
A basic multilayer integral analytical element is described in U.S. Pat. No. 3,092,465. Such multilayer elements use an absorbent carrier impregnated with one or more reagents, typically including a color former, over which is coated a semipermeable membrane. Upon contact with a test liquid, analyte passes through the membrane and into the carrier to generate color in an amount related to the concentration of analyte. The membrane prevents passage and absorption of certain interfering components such as red blood cells, that could impair accurate reading of the color provided as a test result.
Other multilayer integral analytical elements are described in U.S. Pat. No. 3,992,158. Such elements can receive a liquid sample and spread the sample within a spreading layer of the element to obtain in the element an apparent uniform concentration of analyte and produce in the presence of analyte an analytical result that can be measured quantitatively by automated devices, using techniques such as spectrophotometry, fluorimetry, etc.
Test strips are disclosed in U.S. Pat. No. 3,802,842 made by adhering a test layer to a carrier layer by an adhesive material and covering the layers with a mesh. The mesh is heated by various ways, including ultrasonically to bond the mesh layer to the adhesive layer. The layered material is thereafter cut into test strips of the desired size by conventional means. In U.S. Pat. No. 4,061,468, a test strip is shown which is formed by sealing test papers between a synthetic resin film and a mesh and thereafter, in a separate step cutting the laminate into the desired strip width.
Many of the prior known test strips have more than one reagent-bearing carrier matrix or layer. Thus, a reagent strip can contain tests for more than one constituent in a particular liquid sample. For example, a single reagent strip can consist of a reagent-bearing carrier matrix responsive to glucose in urine, and another matrix layer spaced from the first but adjacent thereto and responsive to ketones, such as acetoacetate. Such products are known on the market. Another reagent strip now being marketed contains eight adjacent reagent-incorporated matrices and provides analytical measurements of pH, protein, glucose, ketones, bilirubin, occult blood, nitrite and urobilinogen.
The devices of the prior art have been made by many different techniques, such as by impregnating paper layers, by printing or spraying the reagent composition onto a layer of the carrier material, or by forming films which are solidified.
Where the reagent layer comprises multiple layers, such layers can be maintained in laminar relationship by adhesives which permit fluid passage between layers. It is not always necessary to employ adhesive to adhere one reagent layer to another. In preparing integral analytical elements using film formers, the layers can be preformed separately and laminated to form the overall element. The material of the film layer can be a composition comprising a plasticizer and a polymer suitable to impart dimensional stability. Layers prepared in such a manner are typically coated from solution or dispersion onto a surface from which the dried layer can be physically stripped.
Blush polymer layers can be used as the film layer material. The film is formed on a substrate by dissolving a polymer in a mixture of two liquids, one of which is of a lower boiling point and is a good solvent for the polymer and the other of which is of a higher boiling point and is a nonsolvent or at least a poor solvent for the polymer. Such a polymer solution is then coated on the substrate, and dried under controlled conditions.
The thickness of any reagent layer and its degree of permeability are widely variable and depend on actual usage. Dry thicknesses of from about 5 microns to about 100 microns have been convenient, although more widely varying thickness may be preferable in certain circumstances.
It may be advantageous to incorporate one or more surfactant materials, such as anionic and nonionic surfactant materials, in the reagent layers. They can, for example, enhance coatability of layer formulations and enhance the extent and range of wetting in layers that are not easily wetted by liquid samples in the absence of an aid such as a surfactant.
In general, the present invention deals with the formation of analytical elements, typically multilayer test elements, for detecting a ligand in, or the ligand binding capacity of, a ligand sample. The general structure of such elements includes one or more reagent impregnated layers incorporating a reagent that is responsive to the ligand in the sample, or responsive to the ligand binding capacity of the sample to give a detectable response and a support layer. Other layers can also be present such as spreading layers, radiation diffusing or blocking layers and the like.
The term "ligand" as used herein refers to body fluid constituents and medicaments or other substances present in such body fluids. The following exemplifies a number of such possible ligands. Reagent compositions are known for blood, plasma or serum ligands such as ascorbic acid, bile acids, bilirubin, cholesterol, creatinine, glucose, lactic acid, phospholipids, triglycerides, urea nitrogen (BUN) and uric acid. Also important is the determination of blood chemistry enzyme ligands such as amylase, cholinesterase, creatine phosphokinase (CPK), the dehydrogenases (hydroxybutyric, isocitric, lactic and malic), lipase, phenylalanine, the transaminases (glutamic oxaloacetic and glutamic pyruvic acid), and alkaline phosphatases, gammaglutamyl transpeptidase, leucine aminopeptidase and the erythrocyte enzymes (glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, glutathione reductase and pyruvate kinase). Testing is also possible for blood protein ligands such as albumin, cryoglobins, components of the coagulation and fibrinolytic systems, complement factors and the cellular and serum immune effectors such as interferon and immunoglobins.
Likewise, reagent compositions are known for urine chemistry determinations. In the field of urine chemistry such ligands generally include ascorbic acid, albumin, creatine, creatinine, glucose, bile acids, bilirubin, protein, ketones, occult blood, nitrite, amylase and phenylpyruvic acid. Further details with respect to ligands will be found in U.S. Pat. No. 4,390,343.